The lining of a tunnel generally consists of prefabricated segments (voussoirs) arranged in the form of a plurality of successive rings.
As the tunnel-boring machine advances, a new ring is constructed by successively assembling a plurality of segments against a previously laid ring.
The front face of each new ring (that is to say, the face oriented towards the cutting head of the tunnel-boring machine) serves as a bearing surface for thrust cylinders located at the rear of the tunnel-boring machine shield (that is to say on the opposite side to the cutting head) and intended to exert the thrust necessary to dig the excavated ground.                The laying of the segments is carried out by an erector, that is to say a machine allowing the gripping of a segment from a magazine arranged at the rear of the tunnel-boring machine shield, then its displacement towards its intended location for form the ring. The erector is a component of the tunnel-boring machine shield, located at the rear thereof.        
At present, the erector is generally controlled by an operator in the immediate vicinity thereof, in the area in which the segments are laid.                However, this driving by an operator has several disadvantages.        
On the one hand, the presence of one or several operator(s) in the segment laying area presents a risk for their safety.
On the other hand, the laying time for each segment is high, especially because one or several operator(s) control(s) the position of a segment placed relative to the segments previously laid, and because the possible position adjustments are carried out empirically by said operator(s). This task is also particularly difficult since it imposes multiple displacements to the operator.
It would therefore be desirable to be able to automate the laying of the segments in order, on the one hand, to avoid the presence of operators in the laying area and, on the other hand, to improve the quality and time of the segment laying.
As the erector is a hydraulic machine of great capacity and great range, with operatively important arrows, its positioning is not accurate and repeatable. These defects are accentuated by the high degree of wear and the significant increase in the operating clearances over the service life of the tunnel-boring machine.
Document FR 2 745 327 describes a device for assisting an operator during the laying of segments in a tunnel. This device implements a measuring sensor designed to measure the position of a reference point on a lateral face of a segment previously laid and a reference point on a lateral face of the segment to be laid, these two reference points being to be placed opposite each other. This device further comprises a calculator configured to determine, from the analysis of the deviations in these two reference points, the path of the erector to bring the segment to be laid up into the desired position relative to the segment previously laid.
As a first step, the operator controls the erector to bring it approximately into a position close to that of the segment previously laid. The measuring sensor is placed so that the segment to be laid and the segment previously laid are within its field of vision. The analysis of the deviations in the reference points is then carried out and transmitted to the calculator.
The calculator then calculates the displacement of the erector necessary to bring the segment to be laid into its final position. In this phase, the erector is automatically driven according to the displacement defined by the calculator, without intervention of the operator.
However, this device does not allow fully automating the laying of the segment, the approximate placement remaining performed by an operator. In addition, this device does not allow controlling the quality of laying of the segment (said quality to be considered according to different degrees of freedom). In addition, the measuring sensor is specific to the erector so as to be able to follow it.
Document CN104747213 describes a device for the automated laying of segments. This device comprises two three-dimensional cameras intended to acquire images of a face of the segment to be laid and of the face of a segment previously laid intended to be placed in contact with each other during the laying of the segment. This device further comprises a calculator for analyzing said images to determine an offset between said segments.
As a first step, the segment to be laid is brought into an approximate position compared to a segment previously laid.
As a second step, the cameras acquire images of the faces of the segments intended to be placed vis-à-vis one another.
These images are transmitted to the calculator that processes them to deduce therefrom an offset between the two segments defined on the one hand by the distance between the faces vis-à-vis the two segments and the distance between the front faces of the two segments. If this offset is less than a determined threshold, the segment is considered as correctly positioned and the method for laying said segment is completed. If this offset exceeds said threshold, the calculator determines the movements of the erector necessary to improve the segment positioning accuracy, and the erector is automatically controlled to perform said movements. This procedure can possibly be iterated until the offset between the two segments is below the determined threshold.
However, the times for processing such images are relatively long, which penalizes the time for laying each segment. In addition, this device does not take into account any possible angular offset of the segment to be laid relative to the segment previously laid.
Document JPH08-296400 describes an erector allowing the automated laying of segments comprising a vision sensor consisting of two cameras, one of which has a field of vision greater than that of the other.
As a first step, the segment to be laid is brought into an approximate position relative to a segment previously laid.
A laser projector projects a line of light on the faces intended to be in contact with the segment previously laid and the segment to be laid. The cameras acquire images of said line of light. These images are transmitted to the calculator which processes them to deduce therefrom an offset between the two segments, this offset being defined in position (distances in three directions) and in inclination (angles in three directions). The calculator determines the movements of the erector needed to align the two segments, and the erector is automatically controlled to perform said movements.
However, the erector described in this document has been designed specifically and the automation it provides is therefore not adaptable to an existing erector of a tunnel-boring machine of the market.
Finally, none of the aforementioned documents mentions the placement of the first segment or that of the key (last segment allowing to close the ring in the case of a universal ring), which has a more important complexity of placement.